Darifenacin

Darifenacin extended-release tablets are approved to treat overactive bladder. Here is what that includes:

• Urge urinary incontinence — leaking urine when you feel a sudden, strong need to go
• Urgency — a sudden, hard-to-control urge to urinate
• Urinary frequency — needing to urinate more often than normal

All supported products — Darifenacin, Darifenacin 7.5 mg, and Darifenacin 15 mg extended-release tablets — are approved for this same indication.

Darifenacin is a muscarinic antagonist — it blocks specific chemical receptors in the bladder called M3 receptors. These receptors are responsible for triggering the bladder muscle to squeeze. When darifenacin blocks them, the bladder becomes less reactive, reducing those involuntary contractions that cause urgency and leakage. It has a relatively high preference for M3 receptors over other muscarinic receptor types, which is why it targets the bladder fairly selectively — though M3 receptors also exist in the mouth, gut, and eyes, explaining why dry mouth, constipation, and vision changes can still occur.

In clinical bladder studies, darifenacin increased the volume of urine the bladder could hold before triggering an urge, and reduced how often those uncontrolled contractions happened — confirming its bladder-calming action.

Darifenacin extended-release tablets are taken once daily by mouth. They can be taken with or without food — food does not meaningfully affect how the medicine works when taken regularly. The tablet must be swallowed whole with water and must not be chewed, crushed, or split, as this would disrupt the extended-release design.

• Your prescriber may adjust your dose after the first two weeks if needed
• If you have moderate liver disease or take certain strong CYP3A4 inhibitor medications, your dose will be kept at the lower available strength
• Darifenacin extended-release tablets are not recommended for people with severe liver disease

Always follow your prescriber's specific instructions and the directions on your prescription label.

The most common side effects with darifenacin extended-release tablets include:

• Dry mouth — the most frequently reported side effect
• Constipation — also very common; drink plenty of fluids and eat fiber-rich foods
• Indigestion or upset stomach (dyspepsia)
• Nausea
• Headache
• Urinary tract infection
• Dry eyes
• Dizziness

Most side effects are mild to moderate and tend to appear in the first two weeks of treatment. However, contact your doctor immediately if you experience severe constipation, inability to urinate, confusion, hallucinations, extreme drowsiness, or any swelling of the face, lips, tongue, or throat — these are serious reactions that need prompt attention.

• Angioedema (airway swelling): Rare but life-threatening swelling of the face, lips, tongue, or throat has been reported — even after the first dose. Stop the medicine and seek emergency care immediately if this occurs.
• Urinary retention: Darifenacin can make it harder or impossible to urinate, especially in people who already have bladder outlet problems. Use with caution if you have such conditions.
• Constipation and gut slowdown: The medicine slows the digestive tract. Use with caution if you have severe constipation, bowel obstruction, ulcerative colitis, or myasthenia gravis.
• CNS (brain) effects: Confusion, hallucinations, and excessive drowsiness have been reported. Monitor for these symptoms, especially at the start of treatment or after a dose increase. Do not drive or use heavy machinery until you know how it affects you.
• Narrow-angle glaucoma: Use only with extreme caution if you are being treated for this eye condition — discuss risks and benefits with your doctor.
• Liver disease: People with moderate liver impairment need a lower dose; those with severe liver disease should not use darifenacin.

Darifenacin is broken down by liver enzymes (mainly CYP3A4 and CYP2D6), and it can also affect how other drugs are processed. Key interactions include:

• Potent CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir, nelfinavir, clarithromycin, nefazodone) — raise darifenacin blood levels significantly; the daily dose must be limited to the lower available strength
• Moderate CYP3A4 inhibitors (erythromycin, fluconazole, diltiazem, verapamil) — may raise levels somewhat; no dose change required, but your doctor should know
• CYP2D6 inhibitors (paroxetine, fluoxetine, quinidine, duloxetine) — no dose adjustment required, but awareness is important
• Narrow therapeutic window CYP2D6 substrates (flecainide, thioridazine, tricyclic antidepressants) — darifenacin may raise their levels; use together with caution
• Other anticholinergic medications — combining them increases the risk and severity of side effects like dry mouth, constipation, and blurred vision
• Warfarin and digoxin — no clinically significant interaction found, but routine monitoring for these drugs should continue

This is not a complete list of interactions. Always talk with your doctor or pharmacist before starting, stopping, or changing any medication.

• Do not take if you have urinary retention, gastric (stomach) retention, or uncontrolled narrow-angle glaucoma
• Tell your doctor if you have any bladder outlet obstruction or difficulty urinating
• Tell your doctor if you have any digestive tract blockage, severe constipation, ulcerative colitis, or myasthenia gravis
• Tell your doctor if you have narrow-angle glaucoma that is being managed — use requires careful risk-benefit assessment
• Tell your doctor about any liver problems — dosing limits apply for moderate liver disease, and the medicine is not recommended for severe liver disease
• Pregnancy: Use only if the benefit to the mother clearly outweighs potential risk; animal studies showed some developmental effects at high doses
• Breastfeeding: It is unknown whether darifenacin passes into human milk; discuss with your doctor before nursing
• Children: Safety and effectiveness in pediatric patients have not been established — not for use in children
• Older adults (65+): No dose adjustment is needed; clinical studies showed similar safety and effectiveness compared to younger patients
• Kidney disease: No dose adjustment is needed; studies showed kidney function does not significantly affect how the body clears darifenacin

Taking too much darifenacin can cause severe anticholinergic effects — an exaggerated version of its usual side effects. In clinical trials, doses far above the recommended maximum mainly caused abnormal vision. Treatment focuses on managing symptoms, and ECG monitoring (heart tracing) is recommended in case of overdose.

If you think you or someone else has taken too much, seek emergency medical attention or call Poison Control right away.

In bladder studies involving patients with involuntary bladder muscle contractions, darifenacin increased the amount of urine the bladder could hold before triggering an unstable contraction, and reduced how often those contractions occurred — consistent with its anticholinergic action on the bladder muscle.

At the doses studied, darifenacin extended-release tablets did not prolong the QT interval (an electrical measurement of heart rhythm), which is reassuring for cardiac safety. Small, clinically insignificant changes in heart rate were observed in one study but were not seen in the broader clinical trials.

After taking darifenacin extended-release tablets by mouth, peak blood levels are reached in about 7 hours, and steady, stable levels in the body build up by around day 6 of daily dosing. Food does not meaningfully affect overall drug exposure when taken regularly. Darifenacin is almost entirely bound to proteins in the blood (about 98%) and is extensively processed by the liver using enzymes CYP2D6 and CYP3A4.

The elimination half-life (the time it takes the body to clear half the drug) is roughly 13 to 19 hours with regular dosing, which supports once-daily use. About 60% of the drug leaves the body through urine and 40% through stool. People who are genetically slow CYP2D6 metabolizers ("poor metabolizers") will have higher drug levels than average — an important factor when dosing decisions are made alongside other medications.

Store at 25° C (77°F); excursions permitted between 15°C to 30°C (59°F to 86°F) . Protect from light.